Dual-function semiconducting polymer devices: Light-emitting and photodetecting diodes

Thin film devices made with poly2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene, MEH-PPV, are known to be efficient light-emitting diodes. The same devices, under reverse bias, exhibit excellent sensitivity as photodiodes. Thus the polymer tunnel diode is a dual-function device. For the Ca/MEH-PPV/ITO (indium/tin oxide) layered structure, the external quantum efficiency for electroluminescence is ≊1% photons/electron (forward bias ≳2.5 V). The same device is sensitive as a photodiode: The dc sensitivity (−10 V, reverse bias) is 9×10−2 A/W (at ∼1-μW/cm2 input) corresponding to a quantum yield of more than 20% electrons/photon.